Water soluble organosilanes containing silicon-bonded hydrolyzable groups such as alkoxysilanes have a number of uses. The hydrolyzable groups enable such compounds to permanently attach themselves to substrates containing hydroxyl or other silicon-reactive groups. These organosilanes can be used in waterproofing cement, brick and mortar as well as to provide a further reactive group bonded to various substrates to enable that substrate to be dyed or painted or else to render the substrate antimicrobial or algicidal, among other things, depending upon the nature of the remaining silicon-bonded reactive groups which are not hydrolyzable.
For ecological reasons, it is more desirable to deliver such organosilanes to a substrate from a substantially aqueous medium which contains as few solvents as possible. Organosilanes are often used as coupling agents to improve the bonding of fillers to resins such as the unsaturated polyester resins used to make fiberglass boats, shower stalls and the like and can be applied from aqueous solutions. Page 58 of a brochure from Petrarch Systems of Bristol, Pa., entitled "Silicon Compounds, Register & Review", 1987, states that the stability of aqueous silane solutions varies from hours for the simple alkyl silanes to weeks for the aminosilanes. It states that the alkoxysilane is dissolved at 0.5-2.0% concentration in water. For less soluble silanes, 0.1% of a nonionic surfactant is added just prior to addition of the silane so that an emulsion rather than a solution is formed.
Further comments on the instability in water of organosilanes containing hydrolyzable groups are found in "A Guide to Dow Corning Silane Coupling Agents", Dow Corning Corporation, Midland, Mich., Form No. 23-012B-85 (1985) on pages 6-7 teaching that self-condensation of the silanol form of the organosilane coupling agent to form siloxane polymers is an important side reaction, particularly in aqueous pretreatment solutions and at a pH greater than 7. It teaches that with organosilanes that form water soluble polymers such as aminosilanes, the solution remains effective as a pretreatment. In the case of nonpolar silanes such as methyltrimethoxysilane and 3-chloropropyltrimethoxysilane, it teaches that precipitation can occur on long standing and coupling activity lost. The brochure states that, in such cases, it is especially important to use fresh solutions and to avoid high pH ranges which promote organosilane condensation. Page 11 of a newer version of this brochure published in 1990 as Brochure No. BL40531 teaches that dilute aqueous solutions of silane coupling agents should be prepared fresh daily.
On pages 94-95 of "Research Chemicals Catalog, Chemicals for Research Scientists", from PCR, Inc. of Gainesville, Fla. (1988), an aqueous solution of organosilanes is taught using 0.5-2% organosilane and 99.5-98.0% water along with sufficient acetic acid to obtain a solution a pH of 3.5-5.0 with pH 3.5 being preferred. The acetic acid is said to be unnecessary for aminosilanes. Additionally, 0.1% of nonionic wetting agents can be added to improve the solubility of the organosilanes and wet-out performance. Page 94 states that solution instability is determined by a change from clear solution to hazy. It states that most hydrolyzed organosilanes go through a condensation reaction to form products which are insoluble in aqueous solutions and, at that point, the solution should no longer be used.
Quaternary ammonium functional organosilanes containing hydrolyzable groups such as those sold under the trademark DOW CORNING.RTM. 5772 (3-(trimethoxysilyl)propyldimethyloctadecyl ammonium chloride) by Dow Corning Corporation of Midland, Mich. and REQUAT.RTM. 1977 (3-(trimethoxysilyl)propylmethyldi(decyl) ammonium chloride) by Sanitized, Inc. of New Preston, Conn. have found a large number of uses because of their ability to attach themselves to a wide variety of substrates where the quaternary ammonium functional group then acts as an antimicrobialand algicidal agent. Substrates treated with such quaternized organosilanes have also been noted to, among other things, be easier to clean, possess soil release properties, and cause hair to exhibit a conditioned appearance.
A very attractive medium from which such quaternized organosilanes can be applied is from an aqueous medium as is taught in U.S. Pat. No. 3,817,739 to Abbott et al., but the silicon-bonded hydrolyzable groups present in such quaternized organosilanes tend to cause them to be unstable due to hydrolysis and subsequent polymerization of the quaternized organosilane when there is more than one such hydrolyzable group per molecule. Abbott et al. tested aqueous solutions of 3-(trimethoxysilyl)propyldimethyloctadecyl ammonium chloride at 3 different pH values (3.8, 7.1 and 9.0) to determine if the pH of the solution affected the durability or effectiveness of the resulting organosilane coating. While they found that neutral to alkaline pH values were preferred for algae control effectiveness, there is no comment on the stability of the aqueous solutions of the quaternized organosilane. U.S. Pat. No. 3,730,701 to Isquith et al. describes a method of controlling algae in aqueous media using quaternized organosilanes and U.S. Pat. No. 3,794,736 to Abbott et al. describes the use of certain organosilylamines containing hydrolyzable groups and their salts for inhibiting the growth of bacteria and fungi.
Quaternized organosilanes are often applied from solvent solutions such as lower alcohols and the commercial versions of these quaternized organosilanes are commonly provided as methanolic solutions.
Another alternative is to form a clear microemulsion of a quaternized organosilane using a cosurfactant having an HLB value of at least 1 as is taught in U.S. Pat. No. 4,842,766 to Blehm et al. However, this patent teaches that the methanol-based solvent in which the organosilane is supplied must be removed before blending the quaternized organosilane with the cosurfactant (e.g., a nonionic surfactant can used). If the methanol is not removed, a creamy white emulsion forms which is unstable and will separate into oil and water phases over time. The '766 Patent also teaches that high shear may have to be applied to the mixtures of organosilane and cosurfactant to ensure codispersion. Obviously, this has the disadvantage of requiring a homogenization step to prepare such microemulsions. Blehm et al. teach that almost any surfactant can be employed including anionic, cationic, amphoteric or zwitterionic surfactants as well as nonionic surfactants although nonionic surfactants and compounds such as glycerol, ethylene glycol, propylene glycol and higher monoalcohols such as pentanol, decanol and decanediol are most preferred.
Another patent teaching oil-in-water emulsions containing 3-(trimethoxysilyl)propyldimethyloctadecyl ammonium chloride as well as, optionally, cosurfactants such as nonionic and cationic surfactants, is U.S. Pat. No. 4,631,273 to Blehm et al. These emulsions employ a homogenizer using high shear conditions and teach that the quaternized organosilane does not hydrolyze while it is in emulsion form and thus does not polymerize to an insoluble siloxane. The Examples use ARQUAD.RTM. T27W cationic surfactant which is trimethyl tallow ammonium chloride. However, these emulsions also require a water immiscible liquid such as a polydimethylsiloxane or a mineral oil with which the quaternized organosilane associates. Blehm et al. teach that a sufficient shear force is necessary to form the emulsions they teach and that an Eppenbach mixer did not provide a sufficient amount of such shear.
U.S. Pat. No. 4,847,088 to Blank teaches that the combination of a quaternized organosilane such as 3-(trimethoxysilyl)propyldimethyloctadecyl ammonium chloride with an acid such as citric acid or boric acid in water results in a composition which exhibits synergistic antimicrobial effects. In Table I, Sample III contained water, 3-(trimethoxysilyl)propyldimethyloctadecyl ammonium chloride and ARQUAD.RTM. T2 quaternary ammonium cationic surfactant as a comparative example. According to the manufacturer, ARQUAD.RTM. T2 is a mixture of dicocodimethyl ammonium chloride and trimethyltallow ammonium chloride. Nothing is taught about the pH or the stability of this composition and the patent teaches away from the use of Sample III in favor of compositions containing the acid, the quaternized organosilane and water only, even though the cationic ARQUAD.RTM. T2 surfactant was said to possess antimicrobial properties. Examples 43-46, below, describe the results of an experiment using the same ingredients as were used in Sample III, Table I, of the Blank '088 Patent. The solutions were found to be stable after 4.5 weeks of both room temperature storage and accelerated aging storage at 60 .degree. C. However, the Blank '088 Patent does not suggest that ARQUAD.RTM. T2 should act as a stabilizer for aqueous silane solutions nor does it suggest that the combination of two different types of surfactants is necessary to achieve such storage stability nor does it suggest that such an additive would broaden the pH stability of such solutions.
PCT International Publication No. WO 87/00006 to Schafer teaches a plant microbiocidal compound for plants in the form of an aqueous solution of 3-(trimethoxysilyl)propyldimethyloctadecyl ammonium chloride which can further include a nonionic surfactant and wetting agent such as polyoxyethylene ethers such as TRITON.RTM. X-100 from Sigma Chemical Co. of St. Louis, Mo. or polyoxyethylenesorbitan monooleate such as TWEEN.RTM. 80 from Sigma Chemical Co. Nothing is taught concerning the stability or the pH of the solutions.
U.S. Pat. No. 4,564,456 to Homan teaches a method of treating water to inhibit corrosion and diminish mineral deposition as well as in industrial and household cleaning compositions through the use of cationic organosilanes such as 3-(trimethoxysilyl)propyldimethyloctadecyl ammonium chloride in an aqueous medium where the pH of the medium is neutral or alkaline. The cationic organosilane is intended to stay in the aqueous medium such as a home humidifier reservoir or water cooling system for an extended period of time.
U.S. Pat. No. 4,567,039 to Stadnick et al. teach a hair conditioning composition which uses an organosilane such as 3-(trimethoxysilyl)propyldimethyloctadecyl ammonium chloride as the hair conditioning agent in an aqueous/organic solvent which can further contain nonionic surfactants as solubilizers. A base is used to adjust the pH of the composition to the required alkaline range of from 8 to 10 to cause swelling of the hair. Stadnick et al. teach that when a base is added to adjust the pH to the desired range, the organosilane tends to polymerize and precipitate. Stadnick et al. therefore caution that the composition should be prepared just before use on the hair or packaged as a two part system to avoid this instability problem.
U.S. Pat. No. 4,421,796 to Burril et al. teaches a method of treating textile fibers with an emulsion composition containing a polydimethylsiloxane and a quaternary ammonium functional organosilane to obtain textiles with improved removal of oily soil as well as with antistatic properties.
Canadian Pat. No. 1,217,004 to Hardy teaches an aqueous hypochlorite bleach composition of pH 10 to 12 which is free of anionic surfactants and further contains a C.sub.16 to C.sub.20 alkyl quaternized organosilane such as 3-(trimethoxysilyl)propyldimethyloctadecyl ammonium chloride as a bactericidal additive which renders the surface of a siliceous substrate treated with such a composition antibacterial and easier to clean. The compositions can further contain thickening agents as well as amine oxide or betaine surfactants. Hardy teaches that quaternized organosilanes having alkyl groups with less than 16 carbon atoms tend to be too water soluble and display markedly impaired surface substantivity when used in the presence of hypochlorite stable surfactants. The stability of the quaternized organosilanes in these strongly alkaline compositions is also discussed.
The following patents deal with the inclusion of organosilanes such as 3-(trimethoxysilyl)propyldimethyloctadecyl ammonium chloride in detergent compositions: U.S. Pat. Nos. 4,005,025 to Kinstedt, 4,005,028 to Heckert et al. and 4,005,030 to Heckert et al.
The '025 Patent teaches that the detergent compositions containing anionic surfactants and quaternized organosilanes can be used for cleaning metallic and vitreous surfaces such as toilet bowls and leave behind a soil-releasing coating. It teaches that little or no enhancement of deposition of the quaternized organosilane occurs below a solution pH of 8.5 with a steep rise in deposition over the pH range of 8.5-10.0 and a smaller increase in deposition occurs above pH 10.0. The patent also teaches that aqueous products which have phase instability after 1 day at neutral pH (6.5-7.5) are stable for indefinite periods at higher pH values (pH 10-12). Nonionic surfactants can optionally be included.
The '028 Patent is similar to the '025 Patent, but the detergent composition employs nonionic, zwitterionic or ampholytic detergents along with the quaternized organosilane and prefers the use of nonionic surfactants. Little is said concerning stability and pH.
The '030 Patent is similar to the '025 Patent and consists essentially of a detergent composition containing an anionic surfactant and a quaternized organosilane such as 3-(trimethoxysilyl)propyldimethyloctadecyl ammonium chloride with no restriction on the pH of the compositions.
U.S. Pat. No. 4,797,420 to Bryant teaches a disinfectant formulation based on an alkyl dimethylbenzyl ammonium chloride in water along with a nonionic surfactant and a lower alcohol such as isopropanol. Bryant teaches nothing concerning the further inclusion of water soluble organosilanes into his compositions.
U.S. Pat. No. 4,517,375 to Schmidt teaches aqueous impregnating solutions prepared from hydrolyzed alkyltrialkoxysilanes where the alkyl group can contain from 1 to 4 carbon atoms. The solutions are said to be stable and remain free of turbidity for as long as 80 hours when prepared at room temperature and the pH of the solution is between 1 and 7, preferably between a pH of 2 to 3.5, using a mineral acid or an organic acid to adjust the pH. Aqueous solutions of the present invention are stable for significantly longer periods of time and over a broader range of pH values.
U.S. Pat. No. 4,648,904 to DePasquale et al. teaches aqueous systems containing silanes containing 2 or 3 hydrolyzable groups such as halide or C.sub.1 -C.sub.3 alkoxy groups and one or two hydrocarbyl groups containing from 1 to 20 carbon atoms and an emulsifying agent having an HLB value of from 4 to 15 along with water. DePasquale et al. generally teaches that all types of emulsifying agents can be used, including cationic surfactants, but teaches away from their use to prefer nonionic surfactants which are preferably polyhydroxy materials. DePasquale et al. also teach that the surfactants, particularly the polyhydroxy type such as the SPAN.RTM. sorbitan fatty acid esters and TWEEN.RTM. polyethylene sorbitan fatty acid esters, are hydrolysis inhibitors in the absence of an acid or alkaline medium. In the acid or alkaline medium of masonry such as concrete, the silanes are said to hydrolyze and thus deposit on that substrate. Thus, DePasquale appears to favor a neutral pH medium while the present invention permits the formation of stable aqueous solutions across a wide range of pH values.